Our long-term goals are to understand the function and biology of ionic channels of excitable cell membranes in molecular terms. How do they open and close, how do they recognize permeant ions, what is their 3-dimensional structure, and what are their origins? The major specific aims during this grant period are: 1) To identify specific chemical groups and drug binding sites on Na channels that influence activation or inactivation of the channels. We will study reagents reaction with amino, sulfhydryl, and carboxyl groups and characterize the effects of the veratridine-class of lipid-soluble gating modifiers. 2) To characterize selectivity, gating, and drug modifiability of two less well-understood potassium channels, the inward rectifier and the A current channel. The motivation is to see if evidence for possible evolutionary relatedness between these channels and the delayed rectifier K channel can be found. 3) To understand the ionic selectivity of anion channels, both of the transmitter-activated and transmitter-insensitive type. Better inhibitors for anion channels will be sought. The experiments will use macroscopic voltage clamp and patch clamp on a variety of invertebrate and vertebrate excitable cell, both from the adult and in culture. The research will reveal fundamental properties of these membrane proteins that are central in cellular excitability, volume regulation, and pH regulation.